Physiological effects of elevated plasma corticosterone concentrations in broiler chickens. An alternative means by which to assess the physiological effects of stress.

Research on physical or psychological stress, in order to monitor objective parameters for animal welfare, is usually performed during experimental stress induction. To avoid treatment of animals with physical or physiological stress, addition of the stress-related hormone corticosterone to the drinking water, may serve as a practical alternative to reproducibly investigate hormone-related stress in broiler chickens. Rapid uptake of the hormone and distribution in the bloodstream were affirmed by elevated plasma corticosterone concentrations immediately after start of the treatment. The effect of hormone administration was evaluated by examination of corticosterone-sensitive organs. Comparable to the observations during physiological stress, we found in our model that uptake of endogenous corticosterone reduced body and spleen growth, increased heterophil counts, and decreased formation of antibodies against sheep red blood cells. Furthermore, corticosterone decreased adrenal gland responsiveness, measured by corticosterone production, after a challenge with adrenocorticotropic hormone. The simple performance, and the close relation between circulating corticosterone levels and heterophil counts, makes this an easy and quick method that is sensitive to increased levels of circulating corticosterone from base levels. The changed responsiveness of the adrenal glands to adrenocorticotropic hormone after increased circulating corticosterone levels may be an indication of the coping strategies during stress. Therefore, this test may be a promising tool in the research of adaptation to stress by broiler chickens.